The present invention relates to a belt structure for a pneumatic radial tire and more specifically for a tire suitable for use on aircraft.
It is generally recognized in the tire art that tires suitable for use on aircraft must be capable of operating under conditions of very high speeds and large loads as compared to tires used on automobiles, busses, trucks or similar earthbound vehicles. It is understood, however, that tires for such earthbound vehicles may advantageously be made in accordance with the broad aspects of the invention described herein. As used herein and in the claims, a tire is "suitable for use on an aircraft" if the tire is of a size and load range, or ply rating, specified in either the YEARBOOK OF THE TIRE AND RIM ASSOCIATION, or the YEARBOOK OF THE EUROPEAN TIRE AND RIM TECHNICAL ORGANIZATION, for the year in which the tire is manufactured, or in the current U.S.A. military specification "MIL-T-5041".
It is known in the tire art that a radial tire having a folded belt ply in its belt structure, shows good high speed properties. In order to enhance the high speed properties of a tire, such belt plies are usually folded around a plurality of unfolded belt plies. The folded belt ply effectively reduces the potential for destruction of the belt which can be caused by a separation of the unfolded belt ends from the surrounding rubber.
Finite element analysis shows that if the reinforcing cords of these unfolded belt plies are parallel to the equatorial plane of the tire, a minimum shear stress between the different plies is obtained. Such an orientation of the reinforcing cords is also obtained by replacing the unfolded layers by spirally wound strips. Layers of spirally wound strips lead in addition to a relatively high belt strength for a relatively low number of belt plies.
It is further known that in view of its high modulus and dimensional stability, aramid is particularly advantageous as reinforcing element in high speed tires. As used herein, "aramid" and "aromatic polyamide" are both understood to mean a manufactured fiber in which the fiber forming substance is generally recognized as a long chain synthetic aromatic polyamide in which at least 85% of the amide linkages are attached directly to the two aromatic rings. Representative of an aramid or aromatic polyamide is a poly (p-phenyleneterephtalamide). It is to be noted that aramid has up to now been mostly disregarded as reinforcement of the belt plies when the reinforcing cords make an angle less than 10.degree. to the equatorial plane of the tire; this is due to the fact that aramid lacks the expansion properties required in the shaping and vulcanizing step of the tire.
It is an object of the present invention to provide a belt for a radial tire particularly suitable for use on aircraft and having excellent dimensional stability, a good tread life as well as outstanding high-speed properties.
It is a further object of the present invention to create a tire belt comprising reinforcing cords consisting at least in part of aramid.